Recently, an automobile carries a plurality of batteries connected in series. To monitor the batteries, a battery monitoring system is provided.
The battery monitoring system has a plurality of monitor units connected in series so that a control signal from a micro controller unit is sent in a direction from one end of the series connection to the other end, and a response signal from the monitor units are returned in a direction from the other end to the one end. Such a transmission of the signal is called a daisy chain communication system. In a typical daisy chain communication system, devices are inter-connected one after another to allow data or information to be passed down from a master device to each and every slave devices along the daisy chain path. The main advantages of the daisy chain system are its simplicity and scalability. User can simply add more devices, when needed, with ease when designing the system. This advantage has resulted in the daisy chain system being used in several applications. One key application that is popular with the daisy chain system is a battery operated system in particular stack battery system. The automotive industry designing electric vehicle (EV) or hybrid vehicle (HEV) works on the basis of stack Li-ion batteries. In the EV system, the batteries are stacked to generate the required voltage rail to power the vehicle. These stacked batteries will be required to be monitored closely to make sure operation is safe. As such, battery management system that monitors individual battery voltage is designed. A plurality of battery and a plurality of battery monitor modules must communicate with each other, and more importantly communicate with the system micro-controller to report the status of the batteries. To pass data or information to each device, daisy chain method is normally used.
FIG. 1 shows a basic structure of a conventional battery monitoring system. The system shown in FIG. 1 includes the following elements: controller unit 10; a plurality of monitor devices 20 for monitoring a battery; stacked battery 30; and interconnection wire harnesses 40. Monitor device (N) is working on high voltage domain due to the high number of stacked batteries whereas monitor device (1) is working on low voltage domain. To achieve communication platform, interconnect wire harnesses 40 provided with isolation devices are used for connecting all the monitor devices.
FIG. 2A shows an example of one embodiment of a prior art battery management system. To allow monitor device 20 to communicate with the controller unit 10, lower/upper interface ports DataL 21, DataU 22 are provided for data transmission. In additional since the monitor devices are turned ON or turned OFF by the control of MCU 11, input/output interface ports WakeupL 24; WakeupH 25 and ShutdnL 23; ShutdnH 26 are provided so that all monitor devices in the daisy chain communication system are turned ON or OFF by the controller unit 10. The lower/upper interface ports DataL 21, DataU 22, and the input/output interface ports WakeupL 24; WakeupH 25 and ShutdnL 23; ShutdnH 26 are connected via isolation or contactless devices and wire harness 40 in the system. Each interface port requires a pair of wire harness 43 connected between the neighboring monitor devices. Isolation devices, such as the transformer 41 and photo coupler 42, are used. The controller unit 10, includes a MCU 11 coupled with the first monitor device 16, which serves as a master monitor device in the system. The master monitor device 16 translates MCU 11 data information into daisy chain protocol.
In another embodiment of a prior art battery management system shown in FIG. 2B, a communication conversion device COM 12 is connected in between MCU 11 and the first monitor device 20. The COM device 12 is provided to translate MCU 11 data information into daisy chain protocol after receiving the data from serial peripheral interface 15 or wakeup 13; shutdown interface 14 from the MCU. The conversion by the COM device 12 allows all monitor devices 20 to be configured as slave devices and serve as a way of standardization of monitor devices design platform.
According to FIG. 2A or 2B, the prior art battery management system has a number of problems.
First, controller unit 10 has separate control ports for the data transmission and the wakeup/shutdown transmission. Because of the separate controls, the complexity of designing micro-controller interface, in daisy chain system increases.
Second is the high cost incur to provide several external isolation devices 41 and 42 to separate the data transmission control and the wakeup/shutdown control.
Third is the high cost incur to include more wire harness 43 (up to 6 wire harnesses are needed) when the data transmission control and the wakeup/shutdown control are separated.
The present invention solves these problems and provides a cost effective and robust method of waking up and communicating device MCU with all the related monitor devices in the whole bank of daisy chain devices using only two wires of interconnecting harness.